1. Field of the Invention
This invention relates to a process for automatically controlling fine coal cleaning circuits.
2. Summary of the Prior Art
In the processing of coal into various sizes, the fine uncleaned coal of a 28 mesh.times.0 or 100 mesh.times.0 can be placed in a flotation cell to separate the coal fines from the ash forming impurities. The coal fines collected from the flotation cell are then passed into a filter tub containing a filter to dewater the coal fines. U.S. Pat. No. 4,552,651 illustrates a flotation cell for separating fine coal from ash forming impurities.
In the froth flotation process for removal of fine combustible coal from the unwanted ash-forming minerals, a frother and collector and water are mixed with the coal in flotation cell and the resulting slurry is aerated so that bubbles adhere to the coal and the coal rises to the surface of the cell and is removed. The flotation product (coal slurry) removed from the flotation cell is thereafter passed to a filter for dewatering. Rotating vacuum disc filters pass through the flotation product in a filter tub. A flocculant is added to the filter tub and the coal cakes on the filters during dewatering and is stripped from the filters for downstream processing. (For a discussion of disc filter coal fines dewatering see "Coal Preparation and Unit-Train Loading," Coal Age, pp. 183-199 (July 1972).
In the past, attempts have been made to automatically control the flotation cell performance of this type of fine coal cleaning circuit. U.S. Pat. No. 4,552,651 illustrates one approach to controlling the flotation cell operation.
None of the prior art processes for fine coal cleaning have, however, combined automatic flotation cell performance with an automatic filter control to optimize fine coal cleaning.